Wireless Communication Method and System

ABSTRACT

A wireless communication method includes sending, by a first device in a wireless network, a poll packet (32, 38, 44) for polling a second device in the wireless network. The poll packet includes an address of the second device. The second device receives and at least partially decodes the poll packet. The second device sends a response packet (36, 40, 46) in response to the poll packet. The sending of at least part of the response packet is substantially simultaneous with the receiving of at least part of the poll packet by the second device. Wireless communication systems, transmitters and receivers using the method are also described.

FIELD

The present invention relates to a wireless communication method, forexample a polling method for a wireless optical network.

BACKGROUND

It is known to provide wireless data communications by using visiblelight (or infrared or ultraviolet light) instead of radio frequencies totransmit and receive data wirelessly between devices. Data may betransmitted using visible light by modulating an intensity of the light.The light used may be coherent or incoherent. Wireless networks usingvisible light may in some circumstances allow a higher data capacity andgreater energy efficiency than radio frequency wireless networks, andmay also be used to replace point-to-point infrastructure in locationswhere conventional infrastructure does not exist or is too expensive tobuild.

The IEEE 802.11 standard is a standard for communication over wirelessnetworks. A wireless network may comprise an access point (AP) andseveral stations (STA) which each communicate with the access point. Toallow multiple stations to communicate with a single access point, theIEEE 802.11 standard provides a distributed coordinated function (DCF)multiple access method and a point coordinated function (PCF) multipleaccess method.

In the DCF method, a station wishing to transmit data on a channel waitsuntil the channel is not busy before sending the data. A station maytransmit data to the access point on a channel once it detects that thechannel is not busy for a given time interval. If the data sent by thestation is successfully received, the access point sends anacknowledgement (ACK) to the station. If there are several stations,additional measures may be taken to avoid collisions occurring due toall the stations trying to send data at once when the channel ceases tobe busy.

In the PCF method, the access point polls the stations sequentially. Theaccess point may perform repeated polling cycles. In each polling cycleit may poll each of the stations in order. A given station is permittedto send data to the access point only in response to that station beingpolled. If a station does not have data to send, it must neverthelessrespond to the poll. When an access point receives uplink data from astation it sends an ACK to acknowledge the receipt of the uplink data.When a station receives downlink data from the access point it sends anACK to acknowledge the receipt of the downlink data.

The polling of a station in known PCF methods comprises the sending of apoll packet. The poll packet includes an address of the station to bepolled and a flag that indicates that the station is being polled. Thepoll packet includes a MAC frame comprising a MAC header.

The 802.11 PCF method addresses a device by the MAC address of thatdevice. The MAC address is contained in the 802.11 MAC header inaccordance with the 802.11 standard (see, for example IEEE Std802.11-2012, Part 11: Wireless LAN Medium Access Control (MAC) andPhysical Layer (PHY) specifications). In a poll packet in accordancewith the 802.11 standard, the frame control field of the MAC frame hasthe value for CF-Poll.

The response to a poll message by the station being polled comprisessending a response packet to the access point. The response packet sentfrom the polled station may also include additional payload data or ACKmessages, or may be a minimal response that does not include suchadditional payload data or ACK messages.

The PCF method of the 802.11 standard has to follow a certain timingbecause it is designed to coexist with the standard access method DCF.The 802.11 PCF method must allow time intervals in which devices cantransmit using DCF.

FIG. 1 is representative of a polling cycle on a simple network usingthe 802.11 polling scheme. The network includes one access point (AP)and two stations (STA1, STA2). A timeline 10 is shown, with time goingfrom left to right.

Blocks above the timeline 10 represent downlink packets sent by the AP.Blocks below the timeline 10 represent uplink packets sent by stations.

At block 12, the AP polls the first station, STA1, by sending a pollpacket addressed to STA1. The poll packet is received and decoded atSTA1. Once the complete poll packet has been received and decoded, STA1sends a response packet (represented by block 14) to the AP. Theresponse packet is received and decoded by the AP.

The decoding of a packet refers to the extraction of data from thepacket, and may be used to refer to or comprise demodulation techniquesused to extract data from received signals.

At block 16 (which starts after the response packet of block 14 has beenreceived and decoded), the AP polls the second station, STA2, by sendinga poll packet addressed to STA2. The poll packet addressed to STA2 isreceived and decoded by STA2.

At block 18, after the poll packet addressed to STA2 has been receivedand decoded by STA2, STA2 sends a response packet to the AP. In thisexample, the response packet sent by STA2 at block 18 also carries adata payload.

Poll packets and response packets may carry payload data andacknowledges (ACKs) if there is anything to send. If the response packetcarries a payload of data from a station, a subsequent poll packetaddressing that station may include an ACK acknowledging the receipt ofthat payload data. If payload data is carried in the poll packet, aresponse to that poll packet may comprise an ACK acknowledging thatpayload data.

SUMMARY

In a first aspect of the invention there is provided a wirelesscommunication method, the method comprising: sending by a first devicein a wireless network a poll packet for polling a second device in thewireless network, wherein the poll packet comprises an address of thesecond device; receiving and at least partially decoding by the seconddevice the poll packet; and sending by the second device, in response tothe poll packet, a response packet, wherein the sending of at least partof the response packet by the second device is substantiallysimultaneous with the receiving of at least part of the poll packet bythe second device

The response packet may be sent after decoding of the address. Theresponse packet may be sent before completion of said at least partialdecoding of the poll packet.

A response procedure may be initiated by the second device beforecompletion of said at least partial decoding of the poll packet. Theresponse procedure may comprise the sending of the response packet. Theresponse procedure may comprise modulating and encoding the responsepacket and transmitting the response packet.

The sending of the response packet may initiated before completion ofdecoding of the poll packet, and continue after the completion ofdecoding of the poll packet. The sending of the response packet may beinitiated before completion of decoding of the poll packet and becompleted before completion of decoding of the poll packet.

The decoding may comprise a demodulation process. The second device maysend the response packet as soon as it decodes its address, instead ofdecoding the whole packet before sending the response packet. Sendingthe response as soon as it decodes the address may result in fastercommunications and reduced delays.

The sending of the poll packet may be on a first channel and the sendingof the response packet may be on a second, different channel. The firstchannel and second channel may form a full duplex connection between thefirst device and second device. The first channel may comprise a visiblelight downlink. The second channel may comprise an infrared uplink.

The sending of at least part of the poll packet by the first device maybe substantially simultaneous with the receiving of at least part of theresponse packet by the first device.

By using separate uplink and downlink channels, a full duplex connectionbetween the first device and second device may be formed. Each of thefirst device and second device may receive on one channel at the sametime as transmitting on the other channel. By sending at least part of aresponse packet simultaneously to receiving part of a poll packet, thepolling procedure may be faster than if packets were not sent andreceived simultaneously.

The poll packet may comprise a physical layer (PHY) packet. The pollpacket may comprise at least one header.

The poll packet may comprise a physical layer header, and the address ofthe second device may be provided in the physical layer header. Thephysical layer header may comprise a PHY header, for example a PHYheader under IEEE 802.11.

The poll packet may be addressed using bits of the PHY header. Thenumber of bits in the PHY header that are used to address the pollpacket may determine how many devices may be addressed, for example upto 16 devices.

The packet may further comprise at least one further header, for examplea MAC header, that includes an acknowledgement message. The packet mayalso include an additional MAC frame that carries payload data and thatincludes a further MAC header.

The poll packet may comprise a PHY header and a MAC header. The pollpacket may be a modified PHY packet which comprises a high reliabilityMAC header in addition to a preamble, PHY header and payload. Theaddress may be in the high reliability MAC header.

The poll packet may further comprise payload data and/or anacknowledgement message, and the method may comprise sending by thesecond device the response packet before, or without completing,decoding of the payload data and/or acknowledgement message.

The acknowledgement message may comprise an ACK, for example an ACKunder IEEE 802.11.

The poll packet may comprise at least one portion that is addressed to afurther device.

Said at least one portion may comprise at least one of a payload or anacknowledgement message.

The method may comprise sending by the second device the response packetwithout, or without completing, decoding of the payload data and/oracknowledgement message included in said at least one portion of thepoll message.

A signal for one device may be included in a poll packet addressed to adifferent device. All devices may receive and decode all packets.Including an ACK for one device in a poll packet addressed to anotherdevice may result in faster network operation.

The first device may send a first part of the poll packet using a firstrate and may send a second part of the poll packet using a second,different rate, optionally the first part of the poll packet comprisingthe address of the second device.

The second device may send a first part of the response packet using afirst rate, and may send a second part of the response packet using asecond, different rate.

The values of the first and second rates may be different for theresponse packet than for the poll packet.

The first and second parts may be provided in any order, for examplefirst part before second part or second part before first part.

The first and second rates may comprise first and second modulationrates and/or channel coding rates.

The first rate may be lower than the second rate.

The poll packet or response packet may comprise an acknowledgementmessage, and the acknowledgement message may be provided in the firstpart of the poll packet or response packet. The acknowledgement messagemay comprise an ACK. The acknowledgement message may acknowledge receiptof data, for example a payload.

By including the ACK in the first part of the poll packet which is sentat a lower rate, the ACK may be included in the more reliable part ofthe transmission of the poll packet. It may therefore be more likelythat the ACK will be received even if the transmission channel isdegraded.

The first part of the poll packet may be considered to be a highreliability part of the poll packet. The high reliability part of thepoll packet may be placed first in the poll packet (after the preambleand before any other part of the poll packet). Timing and channelestimation errors may be smallest just after a fine timing estimationand channel estimation which is performed using the preamble.

The first part of the poll packet and/or the first part of the responsepacket may comprise a MAC header, and the acknowledgement message may beprovided in the MAC header.

The first device may be further configured to send subsequent pollpackets to the second device and to at least one further device in arepeating polling sequence.

The first device may poll a plurality of devices in turn. The firstdevice may perform a plurality of polling cycles, each polling cyclecomprising polling the devices in the same order.

The first device may be configured to repeatedly poll the second deviceand at least one further device in a polling order.

Each of the second device and the or each further device may beconfigured to receive and at least partially decode all poll packetssent from the first device.

The first device may be configured to send one or more of the subsequentpoll packets only if the transmission of the first poll packet iscomplete and no packet reception by the first device is occurring.

The method may further comprise aborting by the second device thetransmission of the response packet if the second device receives afurther poll packet from the first device during transmission of theresponse packet.

The reception of any poll packet by the second device while the seconddevice is transmitting may indicate to the second device that the firstdevice is not receiving its transmission. The second device may resendthe response packet in the next polling cycle.

The further poll packet may be addressed to a device other than thesecond device.

The first device may comprise an Access Point (AP) and the second devicemay comprise a Station (STA).

The wireless network may comprise an optical wireless network. Theoptical wireless network may comprise a visible light communication(VLC) network. The wireless network may comprise at least one visiblelight transmission channel.

The sending of the poll packet may comprise sending the poll packetoptically, and/or the sending of the response packet may comprisesending the response packet optically.

The optical wireless network may comprise a downlink between the firstdevice and second device, the downlink having a first wavelength, and anuplink between the first device and second device, the uplink having asecond, different wavelength.

By using an uplink and downlink that use different wavelengths of light,full duplex operation may be achieved. Devices may send and receivepackets simultaneously. The speed of the network may be increased incomparison to a network using half duplex operation.

The wireless network may comprise a visible light downlink between thefirst device and second device and an infrared uplink between the firstdevice and second device. The wireless network may comprise a fullduplex wireless network system.

The poll packet may be sent via the visible light downlink and theresponse may be sent via the infrared uplink.

At least part of the response packet may be sent in response to thedecoding of the address and before completion of said at least partialdecoding of the response packet.

Said poll packet may further comprise a preamble before the address ofthe second device. At least part of the response packet may be sent inresponse to the decoding of at least part of the preamble. At least partof the response packet may be sent before completion of said at leastpartial decoding of the response packet.

The poll packet may be part of a sequence of polling packets addressedto different devices. The sending of the response packet in response tothe decoding of at least part of the preamble may be performed independence on the address of at least one preceding poll packet in thesequence of poll packets.

The method may further comprise sending by the first device a previouspoll packet for polling a further device in the wireless network,wherein the previous poll packet comprises the address of the furtherdevice, and wherein the previous poll packet is sent before the sendingof said poll packet. The method may further comprise receiving and atleast partially decoding by the second device the previous poll packetbefore the receiving and at least partial decoding of said poll packet.The sending of the response packet by the second device may be dependenton the address of the further device and on a polling sequence in whichthe further device comes before the second device.

The first device may send said poll packet after the previous pollpacket without sending any intervening poll packet between the previouspoll packet and said poll packet.

By receiving and decoding the previous poll packet comprising theaddress of the further device, the second device may determine that apacket after the previous packet (i.e. said poll packet) will beaddressed to the second device. Said poll packet may be the next packetto be sent by the first device after the sending of the previous pollpacket.

The second device may respond to the poll packet as soon as it receivesat least part of the preamble of the poll packet. The second device mayrespond to the poll packet without waiting to decode its address. Byresponding to the poll packet without waiting to decode its address,throughput of the network may be improved. Using the address of theprevious poll packet that is sent by the first device immediately beforethe poll packet may limit the possibility for errors in thedetermination of the address of the poll packet by the second device.

The poll packet may be one of a sequence of poll packets for polling thesecond device. The second device may be configured to respond to someand not all of the sequence of poll packets for polling the seconddevice. The second device may be configured to respond to a proportionof the sequence of poll packets for polling the second device. Theproportion may be a predetermined proportion. The proportion may be aselected proportion. The second device may be configured to respond atpredetermined time intervals.

By responding to only some of the poll packets, the speed of the networkmay be increased. Throughput may be improved. By responding to only someof the poll packets, power efficiency of devices (for example, powerefficiency of the second device) may be improved.

In a further aspect of the invention, which may be providedindependently, there is provided a method comprising: sending by a firstdevice in a wireless network a poll packet for polling a second devicein the wireless network, wherein the poll packet comprises an address ofthe second device; receiving and at least partially decoding by thesecond device the poll packet; and sending by the second device, inresponse to the poll packet, a response packet, wherein at least part ofthe response packet is sent before completion of said at least partialdecoding of the poll packet, optionally after decoding of the address.

In another aspect of the invention, which may be provided independently,there is provided a wireless communication method comprisingtransmitting a packet by a first device to at least one further device,the method further comprising transmitting a first portion of the packetusing a first rate and transmitting the second portion of the packetusing a second, different rate. The first and second rates may comprisefirst and second coding or modulation rates. The first portion maycomprise a poll or a poll response. The second portion may comprise anacknowledgement message and/or a payload.

In a further aspect of the invention, which may be providedindependently, there is provided an optical communication method, themethod comprising sending by a first device in an optical wirelessnetwork a poll packet for polling a second device in the opticalwireless network, wherein the poll packet comprises the address of thesecond device, and wherein the poll packet comprises at least oneportion that is addressed to a further device.

In another aspect of the invention, which may be provided independently,there is provided a wireless communication method, the methodcomprising: sending by a device in a wireless network a packet to aplurality of further devices; wherein the packet comprises a firstportion that is addressed to a first one of the further devices and asecond portion that is addressed to a second one of the further devices,and the method further comprises sending the first portion of the packetat a first rate and sending the second portion of the packet at asecond, different rate.

In a further aspect of the invention, which may be providedindependently, there is provided a wireless communication systemcomprising: a first device configured to transmit a poll packet forpolling a second device, the poll packet comprising an address of thesecond device; and the second device, wherein the second device isconfigured to: receive and at least partially decode the poll packet;and to send, in response to the poll packet and substantiallysimultaneously with the receiving of at least part of the poll packet, aresponse packet.

The second device may be configured to send at least part of theresponse packet after decoding of the address. The second device may beconfigured to send at least part of the response packet beforecompletion of said at least partial decoding of the poll packet.

The wireless communication system may be configured to perform a methodas claimed or described herein.

In another aspect of the invention, which may be provided independently,there is provided a transmitter configured to transmit a poll packet forpolling a further device, the poll packet comprising an address of thefurther device included in a physical layer header of the poll packet.

In a further aspect of the invention, which may be providedindependently, there is provided a receiver configured to receive and atleast partially decode a poll packet, and to send a response packet inresponse to the poll packet after decoding of an address of the pollpacket and before completion of said at least partial decoding of thepoll packet.

In another aspect of the invention, which may be provided independently,there is provided a poll packet, the poll packet including an address ofa device to be polled in a physical layer header of the poll packet.

There may also be provided an apparatus or method substantially asdescribed herein with reference to the accompanying drawings.

Any feature in one aspect of the invention may be applied to otheraspects of the invention, in any appropriate combination. For example,apparatus features may be applied to method features and vice versa.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the invention are now described, by way of non-limitingexamples, and are illustrated in the following figures, in which:—

FIG. 1 is a schematic diagram representative of an AP polling two STAsusing an 802.11 PCF polling scheme;

FIG. 2 is a schematic illustration of an optical wireless networkaccording to an embodiment;

FIG. 3 is a schematic diagram representative of an AP polling two STAsusing a polling scheme in accordance with an embodiment;

FIG. 4 is a schematic diagram representative of a PHY packet format;

FIG. 5 is a schematic diagram representative of a PHY packet format inaccordance with an embodiment.

FIG. 2 shows an embodiment of an optical wireless network in which oneaccess point 20 (AP) may send data to and receive data from each of twostations 22 and 24 (STA1 and STA2). Although only two stations are shownin FIG. 2, in other embodiments any appropriate number of stations maybe present in the optical wireless network. The optical wireless networkmay comprise multiple access points, with each AP being opticallyconnected to one or more stations.

The access point 20 comprises a light source 25 which may be used tosend data by modulation of light. In the present embodiment, the lightsource is an LED lamp. In other embodiments, the light source may be anyappropriate coherent or incoherent light source, for example a laserlight source. The access point 20 also comprises a light detector 26(for example, a photodiode) that may be used to receive modulated light.The access point 20 is configured to decode the received light to obtaindata. Each of the stations 22, 24 also comprises a light source 27 a, 27b and a light detector 28 a, 28 b. Different devices (access point 20,station 22, station 24) may have the same or different light sourcesand/or light detectors.

Each of the access point 20 and stations 22, 24 also includes a suitableprocessing resource (not shown) for processing received data or data tobe transmitted and suitable encoding/decoding and/ormodulation/demodulation circuitry (not shown), for example processingresources and circuitries configured to implement IEEE 802.11transmission schemes. The processing resource may comprise software,hardware or any suitable combination of software and hardware and, forexample, may include one or more ASICs or FPGAs.

In the present embodiment, downlink data (data sent from the accesspoint 20 to one of the stations 22, 24) is sent using visible light.Light source 25 is configured to transmit visible light and lightdetectors 28 a, 28 b are configured to receive visible light. Uplinkdata (data sent from one of the stations 22, 24 to the access point 20)is sent using infrared light. Light sources 27 a, 27 b are configured totransmit infrared light and light detector 26 is configured to receiveinfrared light.

In other embodiments, any suitable frequency or frequencies of light(for example, including infrared, visible or ultraviolet light) may beused for the uplink and downlink. For example, any electromagneticradiation with a wavelength between 10 nm and 2500 nm may be used, withdifferent wavelengths being used for uplink and downlink.

Using different frequency bands (for example, visible and infrared) foruplink and downlink may allow for full duplex operation. Any one of theaccess point 20 or stations 22, 24 may receive and transmit datasimultaneously. For example, the access point may receive uplink datathat is sent using infrared light while sending downlink data usingvisible light.

In the embodiment of FIG. 2, the access point 20 is connected to a wireddata link, for example to an Ethernet link (not shown). The stations 22,24 may be each be connected to or be part of a computer or other device(not shown). For example, each station may be connected to or form partof a mobile communications device such as a cellphone, laptop computeror tablet computer.

Data is sent between the access point and stations using physical layer(PHY layer) packets. A PHY layer packet may comprise a preamble 50, PHYheader 52 and payload 54, as illustrated in FIG. 4. The payload maycomprise any appropriate Media Access Control layer (MAC layer) frame,for example a data frame. The MAC layer frame comprises a MAC header,which may be referred to as a normal MAC header or 802.11 MAC header (incontrast with a high reliability MAC header which is described below).

In the 802.11 standard, the PHY header comprises one OFDM symbol. ThePHY header of the 802.11 standard does not comprise address information.

In the present embodiment, a PHY header is used that may be described asa modified version of an 802.11 PHY header. In the PHY header that isused in this embodiment, a number of bits of the PHY header are freedup, and are then used to represent address information.

In the 802.11 standard, 4 bits of the PHY header are used to includemodulation type and channel coding rate information. Each availablecombination of modulation type and channel coding rate may be referredto as a mod/rate pair. In 802.11, 8 mod/rate pairs are available.

The 8 mod/rate pairs used in 802.11 are encoded in 4 bits in the 802.11standard. However, it is possible to encode the 8 mod/rate pairs in 3bits. In the present embodiment, the 8 mod/rate pairs are encoded in 3bits. Therefore one bit becomes free for use in addressing.

The 802.11 standard allows payloads between 1 and 4095 bytes. In thepresent embodiment, the payload length is a multiple of 32 bits and themaximum length is around 1500 bytes due to a common 1500 byte payloadlimit in networks. Therefore, the MSB (most significant bits) and thetwo LSBs (least significant bits) that are used for the payload lengthin 802.11 become free for use in addressing in the present embodiment.

Four bits of the PHY header are released for use in the presentembodiment (one mod/rate bit and three bits from payload length). Thefour bits that are released are used to encode address data. Thereforethe number of STAs that may be addressed in the PHY header is limited to16. In other embodiments, different circumstances (for example, adifferent maximum payload length) may result in a different number ofbits in the PHY header being available for addressing.

In the present embodiment, a first part of each PHY packet comprisingthe preamble and the PHY header is sent at a first transmission rate,and a second part of each PHY packet comprising the payload is sent at asecond, faster transmission rate. The first transmission rate maycomprise a first modulation rate and/or channel coding rate. The secondtransmission rate may comprise a second modulation rate and/or channelcoding rate. The first part of the packet is sent at a slowertransmission rate so that the sending of the first part of the packet ismore robust than the sending of the second part of the packet. In otherembodiments, the first part and second part of the packet may be sent atthe same transmission rate. In further embodiments, any two or moreparts of the packet may be sent at different rates.

FIG. 3 is a timing diagram illustrating a polling method in accordancewith an embodiment. The polling method is implemented on a networksimilar to that of FIG. 2, which comprises one access point (AP) and twostations (STA1, STA2). In other embodiments, up to 16 stations may bepolled by one access point. The access point may poll all the stationsin the network in turn.

The polling method of the present embodiment makes use of the separateuplink and downlink frequencies to provide a method which may be fasterthan the 802.11 PCF method when used in optical communications.

A timeline 30 is represented in FIG. 3. Time on timeline 30 runs fromleft to right. Blocks above the timeline 30 represent downlink packetssent by the AP. Blocks below the timeline 30 represent uplink packetssent by the stations.

At block 32, the AP polls the first station, STA1, by sending a pollpacket addressed to STA1. The address of STA1 is encoded in the PHYheader of the poll packet. The poll packet comprises payload datad1_down.

In the present embodiment, the AP sends a first part of the poll packetcomprising the preamble and the PHY header at a first transmission rate,and sends a second part of the poll packet comprising the payload datad1_down at a second, faster transmission rate.

Both stations STA1 and STA2 start to receive and decode the poll packetof block 32. Once it has decoded the PHY header, station STA1 knows thatthe poll packet is addressed to it. Arrow 34 indicates the time point atwhich the PHY header has been decoded. Station STA2 determines that thepoll packet is not addressed to it and takes no action at this stage.

As soon as STA1 has decoded the PHY header and determined from theaddress included in the PHY header that the poll packet is addressed toit, STA1 sends a response packet as a response to the poll from the AP.This poll response is illustrated by block 36. STA1 does not wait untilthe poll packet of block 32 has been completely received and decodedbefore sending the response packet. STA1 is able to send a responsepacket while still receiving and decoding the poll packet. The APreceives and decodes the poll response from STA1 while the AP is stilltransmitting the poll packet. The poll response of block 36 does notinclude payload data in this example. The entire response packet ofblock 36 is received by the AP while the AP is still transmitting thepoll packet.

In the example of FIG. 3, the AP finishes sending the first poll packet(block 32) after it has received the poll response from STA1 (block 36).The AP determines that it has finished transmitting and that no packetreception is ongoing. The AP therefore proceeds to send a second pollpacket (block 38). This time the poll packet is addressed to STA2 anddoes not include payload data.

The stations STA1, STA2 receive and decode the second poll packet 38.STA2 determines from the PHY header that the second poll packet isaddressed to it and sends a response packet (shown by block 40) withoutwaiting to receive and decode the rest of the second poll packet. Inthis example, STA2 also sends data d2_up in the poll response packet ofblock 40.

The sending of the poll response packet of block 40 is initiated whilethe second poll packet 38 is being sent, and continues after the sendingof the second poll packet is finished.

The AP waits till both transmission (block 38) and reception (block 40)are complete. In this example, reception of the response packet of block40 lasts longer than the transmission of the poll packet of block 38, sothe AP waits until the reception is complete. A point at whichtransmission and reception are complete is indicated on FIG. 3 by arrow42.

The AP then sends a third poll packet which is addressed to STA1 (block44). The sending of the third poll packet to STA1 may be considered tobe the start of a second polling cycle, where each polling cyclecomprises polling STA1 and polling STA2.

The third poll packet (block 44) comprises an acknowledgement (ACK) ofreceipt of data d2_up which has been received (block 40) from STA2. TheACK is intended for STA2 even though the poll packet is addressed toSTA1. An ACK for STA2 may be carried in a poll packet addressed to STA1,because all stations receive and decode all poll packets, and thus STA2will be able to receive and decode the ACK intended for it.

In the present embodiment, all stations receive and decode all pollpackets and may discard any received information that is unneeded.However, in alternative embodiments, a receiver of a given STA may bestopped once an address of a packet tells the STA that the payload ofthat packet is for another STA (and therefore is not for the given STA).Stopping the receiving of the packet by the given STA once the given STAhas established that the packet is not addressed to it may be used forpower saving, for example power saving in mobile devices.

At block 46, STA1 responds to the third poll packet (block 44). STA1responds to the third poll packet by sending a response packet as soonas it has decoded the PHY header of the third poll packet which isaddressed to it, and without waiting to decode the whole of the thirdpoll packet. STA1 includes in its poll response an acknowledgement (ACK)of the data d1_down that was sent in the first poll packet addressed toSTA1.

Although not illustrated in FIG. 3, the AP continues to send pollpackets alternately to STA1 and STA2. The AP sends a next poll packetwhen its previous transmission of packets has finished and no packetreception is ongoing.

In general, if the AP sends a downlink packet to an STA in one pollingcycle, that STA acknowledges the downlink packet at the next pollingcycle.

When an STA is polled, it sends an uplink packet to the AP as a responseto the polling. The uplink packet may also contain additional payloaddata. The subsequent ACK for the payload data in this uplink packet isthen provided in the next poll packet sent by the AP, even if the nextpoll packet is addressed to a station that is different from the stationthat sent the uplink packet. All stations receive all poll packets.

In some circumstances, a packet may be lost. This situation may beconsidered with reference to FIG. 3. As already described, the APtransmits a first poll packet (block 32) that also contains payload data(d1_down) to STA1. When the AP is ready to transmit a further pollpacket (block 44) to STA1, the AP does not yet know whether the data(d1_down) sent to STA1 in the first poll packet has been received or not(as can be seen from FIG. 3, the ACK in respect of receipt of d1_down isonly sent at block 46). Although STA1 sent a response packet onreceiving the PHY header of the first poll packet (block 32) it ispossible that the PHY header was received correctly by STA1 but that therest of the packet (including data d1_down) was not. For datatransmitted to STA1 in the first polling cycle, the AP cannot receive anACK for that data from STA1 until the second polling cycle.

The AP goes ahead and transmits the further poll packet (in this case,the third poll packet) without knowing whether the first poll packet wasreceived correctly. If no ACK for the first poll packet is received atblock 46, the AP transmits the first poll packet again at a subsequentpolling cycle.

Considering packet loss more generally, consider a situation in whichthe AP has to transmit packets p1 and p2 to one station (for example, toSTA1). Each of packets p1 and p2 may contain payload data. When the APis ready to transmit p2, it still does not know if p1 went through ornot, so it just goes ahead and transmits p2. If no ACK for p1 isreceived, the AP will transmit p1 again (in a further polling cycle).Therefore, the STA may receive the packets in the wrong order, e.g. p2,p1. If this happens, packets can be sorted by the STA, for example usingsequence numbers such as sequence numbers issued by the mac80211 stackor by using any other suitable sorting technique.

In the present embodiment, a STA aborts an ongoing transmission if itreceives any poll packet (whether addressed to it or not). The abortingof the ongoing transmission accounts for the case of a packet receptionfailure at the AP. If packet detection on the AP fails, the AP is notaware of an ongoing uplink packet and sends the next poll packet.Consider, for example, blocks 38, 40 and 42 of FIG. 3. If the AP doesnot receive the response packet of block 40, the AP may send the pollpacket 42 before STA2 has finished transmitting the response packet ofblock 40. STA2 aborts the transmission of the response packet of block40 on receiving the poll packet of block 44. In such circumstances, thetransmitting STA aborts the ongoing uplink packet in order to avoidcorruption of the channel. The aborted packet is resent by the STA atthe next polling cycle.

In the method illustrated in FIG. 3, a station responds to a poll fromthe AP as soon as it recognizes its address in the PHY header.Responding as soon as it recognises its address may be faster and morereliable than a method in which a station must receive and decode theentire poll packet (possibly including a substantial data payload)before responding to the poll packet.

It may be seen in FIG. 3 that the downlink packets overlap in time withthe uplink packets, using the channel in full duplex mode. The pollingscheme shown in FIG. 3 may be described as a modified full duplexpolling scheme. The PCF multiple access method is modified for fullduplex operation because optical communications systems often use visuallight for the downlink and infrared radiation for the uplink, allowingfull duplex operation. A bidirectional PCF algorithm is thereforeprovided. The algorithm of the present invention is a full duplexalgorithm in which a device may receive a poll packet and send aresponse packet simultaneously, or send a poll packet and receive aresponse packet simultaneously.

Unlike 802.11, no coexistence with DCF is required. Therefore, there isno need to observe a certain timing. The AP and STAs may send thepackets as fast as they can. The polling scheme may enable theimplementation of full duplex Time Division Multiple Access (TDMA) forthe optical communication system.

The method described with reference to FIG. 3 may scale well to userdemand. Assume STA1 is idle and STA2 has lots of data. STA2 can usealmost the whole capacity of the network, sending and receiving longdata packets while STA1 receives and sends only poll packets and pollresponse packets. If STA1 also has data, STA1 may occupy more of thechannel capacity while the throughput for STA2 is reduced. If both STAsdemand more throughput than is possible, each STA will get about 50% ofthe capacity, assuming that the same modulation is used for both STAs.

In the embodiment described above with reference to FIG. 3, an addressof the STA that is being addressed in a poll packet is contained in thePHY header of the poll packet using bits of the PHY header.

In an alternative embodiment, the PHY packet format is different fromthat illustrated in FIG. 4. The alternative PHY packet format isillustrated in FIG. 5. A high reliability MAC header is added to the PHYpacket format, in addition to the PHY header. The high reliability MACheader is in addition to the MAC header in the MAC layer frame. In thepresent embodiment, the high reliability MAC header is 1 OFDM symbollong. In some embodiments, the PHY packet with the high reliability MACheader may be used for any wireless communications, whether or not thechannel is full duplex.

A first part of a packet including a preamble 50 and PHY header 52 maybe sent at a first modulation rate and/or channel coding rate, and asecond part of the packet including a payload 54 may be sent at asecond, faster modulation rate and/or channel coding rate.

However, sending packet acknowledgements at a high order modulation mayincrease the probability of a loss of the ACK. Loss of the ACK may causeretransmission of the corresponding payload (the payload that the ACKwas supposed to acknowledge).

A loss of a packet that contains both an ACK and a payload may cause twoadditional transmissions to be required, one for the payload that theACK was supposed to acknowledge, and one for the payload that has beenlost in the lost packet.

If, for example, the downlink channel experiences a degradation, theuplink may also be greatly affected due to the lost ACKs. If ACKs arelost on the degraded downlink channel, the STAs do not know that theiruplink packets have been received and therefore need to resend them,slowing the uplink channel.

In the embodiment of FIG. 5, and in a variant of FIG. 3, ACKs may beplaced in the high reliability MAC header 60. The headers (PHY header 52and high reliability MAC header 60) are sent at the lowest possiblemodulation and channel coding rate (BPSK, r=1/2) which means that thereception of the PHY header 52 and high reliability MAC header 60 islikely to be reliable. Even if the payload is corrupted, the ACK maystill be received correctly. In the present embodiment, the second partof the packet, including the payload, is sent at the highest rate thatthe channel allows.

It may be that a coupling between downlink and uplink performance isreduced or eliminated by use of the different transmission rates forACKs and payloads, for example a coupling between the level ofdegradation of the downlink channel and a level of degradation of theuplink channel. A downlink degradation like reduced SNR (signal to noiseratio) due to misalignment may have very little effect on the uplink andvice versa. A cause of degradation that affects only one of uplink ordownlink may not also affect the other due to missed ACKs. There may besome reduction in throughput due to the introduction of the additionalheader (the high reliability MAC header 60) but, at least in somecircumstances, the benefit of the reliable ACK transmission may outweighthe minor reduction in throughput.

The robustness of 802.11 PCF or of the full duplex method describedabove with relation to FIG. 3 may be improved by the modification of thePHY packet format to include the high reliability MAC header 60.

In further embodiments, the high reliability MAC header 60 may be usedfor other purposes. For example, the high reliability MAC header 60 maybe used for addressing the STAs. In the embodiment described above withrelation to FIG. 3, the STAs are addressed by reusing bits in the PHYheader. Addressing the STAs using bits in the PHY header may limit thenumber of STAs to 16. Addressing the STAs in the high reliability MACheader 60 rather than the PHY header 52 may increase the number of STAsthat can be addressed by one AP while retaining benefits of includingthe address in a header. An STA may respond to its address in a headerbefore it decodes the rest of the poll packet. By including the addressin the high reliability MAC header rather than in the normal MAC headerwhich is part of the MAC frame in the payload, the STA does not have todecode the payload in order to obtain its address.

In the embodiment of FIG. 3, a STA responds to a poll packet as soon asit decodes its address. In further embodiments, the STA responds to apoll packet addressed to it as soon as it receives the preamble of thepoll packet, without waiting to receive the address of the poll packet.

In one such embodiment, a different polling response logic is used fromthat described above with reference to FIG. 3.

Each STA learns the polling sequence used by the AP and knows when itsturn is in the sequence. Therefore, each STA can learn when to expect apoll packet to be addressed to it by using the address of at least oneprevious poll packet. When a STA receives a packet addressed to the STAthat is immediately before it in the sequence, it sends a responsepacket in response to the next poll packet. It sends that responsepacket on decoding the preamble of the next poll packet, withoutdecoding the rest of the next poll packet. The response packet istherefore sent without decoding the address of the poll packet to whichit is responding.

In one example, four STAs are connected to an AP. The four STAs have STAaddresses 0, 1, 5 and 6. The AP polls each of the STAs in turn, i.e. theAP polls STA 0 first, STA 1 second, STA 5 third and STA 6 fourth in eachcycle.

Each STA receives all packets sent by the AP. The STA with address 5knows that after it has received a packet addressed to STA 1, the nexttime slot is the one in which it (STA 5) is going to be polled.Therefore, after STA 5 has received a poll packet addressed to 1, itsends a poll response when it detects the preamble of the next pollpacket. STA 5 does not even wait until it has received its own addressbefore sending a response packet, because it knows from receiving thepacket addressed to STA1 that the next packet in turn should beaddressed to STA 5.

By sending a poll response at the detection of the preamble of thepacket addressed to it, downlink and uplink packets overlap more andthroughput may be increased.

In one embodiment, a given STA uses only the address of the STA that isbefore it in the sequence to determine when it is going to be polled. Inthe example above, when STA 5 receives a poll packet addressed to STA 1,it determines that the next poll packet will be addressed to it (STA 5).In other embodiments, a given STA may use the addresses of multiple STAsto determine when it is going to be polled. For example, when STA 5 hasreceived a poll packet addressed to STA 0 followed by a poll packetaddressed to STA 1, it determines that the next poll packet will beaddressed to it (STA 5).

In some embodiments in which an STA determines the address of a pollpacket addressed to it by using the address of at least one previouspoll packet, addresses are not included in a PHY header or other headerbefore the payload (for example, a high reliability MAC header). Even inembodiments in which the address is not included in the PHY header or ina high reliability MAC header, an STA does not have to wait to receiveand decode the whole of a poll packet addressed to it before itresponds. It determines that the poll packet is addressed to it by usingthe address of at least one previous packet. Therefore it responds tothe poll packet addressed to it as soon as it receives the preamble ofthe packet addressed to it, and before it decodes its address in thatpoll packet.

In a further embodiment, each STA only responds to some of the pollpackets addressed to it, instead of responding to every poll packetaddressed to it. If there is no uplink data or ACK for a given stationto transmit, that STA responds to poll packets only one in a while. Forexample, the STA may respond just often enough to let the AP know thatit is still present. The STA may respond to a predetermined proportionof the poll packets addressed to it, for example to every fifth pollpacket that is addressed to it. Alternatively, the STA may respond atpredetermined time intervals.

Responding to only some of the poll packets may increase throughput,since AP poll packets may be spaced more closely if no response to eachpoll packet is received. Responding to only some of the poll packets mayimprove power efficiency of the STA. Improving power efficiency may beimportant for mobile devices.

Whilst components of the embodiments described herein have beenimplemented in software, it will be understood that any such componentscan be implemented in hardware, for example in the form of ASICs orFPGAs, or in a combination of hardware and software. Similarly, some orall of the hardware components of embodiments described herein may beimplemented in software or in a suitable combination of software andhardware.

It will be understood that the present invention has been describedabove purely by way of example, and modifications of detail can be madewithin the scope of the invention. Each feature disclosed in thedescription, and (where appropriate) the claims and drawings may beprovided independently or in any appropriate combination.

1-34. (canceled)
 35. A wireless communication method, the methodcomprising: sending by a first device in a wireless network a pollpacket for polling a second device in the wireless network as part of apolling sequence that polls the second device and at least one furtherdevice, wherein the poll packet comprises an address of the seconddevice; receiving and at least partially decoding by the second devicethe poll packet; and sending by the second device over a channel of thewireless network, in response to the poll packet, a response packet,wherein: the sending of at least part of the response packet by thesecond device is substantially simultaneous with the receiving of atleast part of the poll packet by the second device; the channel is alsoused by said at least one further device for sending response packets;and the capacity of the channel is shared by the second device and theat least one further device for sending packets that comprise payloaddata and/or acknowledgement messages.
 36. A method according to claim 1,wherein at least part of the response packet is sent before completionof said at least partial decoding of the poll packet.
 37. A methodaccording to claim 1, further comprising: as part of the pollingsequence, sending by the first device to the further device or one ofthe further devices a previous poll packet before said sending of thepoll packet; receiving and at least partially decoding by the seconddevice the previous poll packet before the receiving and at leastpartial decoding of said poll packet, wherein the sending of theresponse packet by the second device is dependent on the address of thefurther device and on the polling sequence, in which the further devicecomes before the second device.
 38. A method according to claim 3,comprising determining by the second device that said poll packet willbe addressed to the second device based on the polling sequence
 39. Amethod according to claim 3, wherein the second device detects apreamble of the poll packet and sends the response packet in response tosaid detection without waiting to receive its own address by thedecoding of the poll packet.
 40. A method according to claim 1, whereinthe sending of the response packet by the second device is after adetecting of the poll packet by the second device and before the atleast partial decoding of the poll packet by the second device.
 41. Amethod according to claim 1, wherein at least one of: a) the pollingsequence comprises or is included in a point coordinated function (PCF)multiple access polling scheme modified for full duplex operation; b)the first device comprises an access point, the second device and the atleast one further device each comprise a respective station, and thepolling sequence comprises or is included in a polling scheme forallowing multiple stations to communicate with a single access point.42. A method according to claim 1 wherein at least one of: a) theresponse packet comprises an acknowledgement message; b) the wirelessnetwork comprises an optical wireless network; c) the polling sequencecomprises a repeating polling sequence.
 43. A method according to claim1, wherein the sending of the poll packet is on a first channel and thechannel on which the response packet is sent is a second, differentchannel.
 44. A method according to claim 9, wherein the first channeland second channel form a full duplex connection between the firstdevice and second device.
 45. A method according to claim 9, wherein thefirst channel comprises a visible light downlink and the second channelcomprises an infrared uplink.
 46. A method according to claim 1, whereinthe poll packet comprises a physical layer (PHY) packet.
 47. A methodaccording to claim 12, wherein the poll packet comprises a physicallayer header, and the address of the second device is provided in thephysical layer header.
 48. A method according to claim 1, wherein thepacket further comprises at least one further header, for example a MACheader, that includes an acknowledgement message.
 49. A method accordingto claim 1, wherein the poll packet further comprises payload dataand/or an acknowledgement message, and the method comprises sending bythe second device the response packet before, or without completing,decoding of the payload data and/or acknowledgement message.
 50. Amethod according to claim 1, wherein the poll packet comprises at leastone portion that is addressed to a further device.
 51. A methodaccording to claim 16, wherein said at least one portion comprises atleast one of a payload or an acknowledgement message.
 52. A methodaccording to claim 1, wherein the sending of the poll packet by thefirst device comprises sending a first part of the poll packet using afirst rate and sending a second part of the poll packet using a second,different rate, the first part of the poll packet comprising the addressof the second device.
 53. A method according to claim 1, wherein thesending of the response packet by the second device comprises sending afirst part of the response packet using a first rate, and sending asecond part of the response packet using a second, different rate.
 54. Amethod according to claim 19, wherein the first and second ratescomprises first and second modulation rates and/or channel coding rates.55. A method according to claim 19, wherein the first rate is lower thanthe second rate.
 56. A method according to claim 19, wherein the pollpacket or response packet comprises an acknowledgement message, and theacknowledgement message is provided in the first part of the poll packetor response packet.
 57. A method according to claim 22, wherein thefirst part of the poll packet or the first part of the response packetcomprises a MAC header, and the acknowledgement message is provided inthe MAC header.
 58. A method according to claim 1, wherein the firstdevice is further configured to send subsequent poll packets to thesecond device and to said at least one further device in the repeatingpolling sequence.
 59. A method according to claim 24, wherein the firstdevice is configured to send one or more of the subsequent poll packetsonly if the transmission of the first poll packet is complete and nopacket reception by the first device is occurring.
 60. A methodaccording to claim 24, further comprising aborting by the second devicethe transmission of the response packet if the second device receives afurther poll packet from the first device during transmission of theresponse packet.
 61. A method according to claim 1, wherein the wirelessnetwork comprises a visible light downlink between the first device andsecond device and an infrared uplink between the first device and seconddevice.
 62. A method according to claim 1, wherein at least part of theresponse packet is sent in response to the decoding of the address andbefore completion of said at least partial decoding of the responsepacket.
 63. A method according to claim 1, wherein said poll packetfurther comprises a preamble before the address of the second device,and wherein at least part of the response packet is sent in response tothe decoding of at least part of the preamble.
 64. A method according toclaim 29, wherein the poll packet is part of a sequence of pollingpackets addressed to different devices, and the sending of the responsepacket in response to the decoding of at least part of the preamble isperformed in dependence on the address of a least one preceding pollpacket in the sequence of poll packets.
 65. A method according to claim1, wherein said poll packet is one of a sequence of poll packets forpolling the second device, and wherein the second device is configuredto respond to some and not all of the sequence of poll packets forpolling the second device.
 66. A wireless communication systemcomprising: a first device configured to transmit a poll packet forpolling a second device, the poll packet comprising an address of thesecond device as part of a polling sequence that polls the second deviceand at least one further device; and the second device, wherein thesecond device is configured to: receive and at least partially decodethe poll packet; and to send, in response to the poll packet andsubstantially simultaneously with the receiving of at least part of thepoll packet, a response packet over a channel of a wireless network,wherein the channel is also used by said at least one further device forsending response packets, and the capacity of the channel is shared bythe second device and the at least one further device for sendingpackets that comprise payload data and/or acknowledgement messages. 67.A receiver configured to receive and at least partially decode a pollpacket, and to send a response packet in response to the poll packetover a channel of a wireless network, wherein the sending of at leastpart of the response packet by the receiver is substantiallysimultaneous with the receiving of at least part of the poll packet bythe receiver; and the channel is also used by at least one furtherdevice for sending response packets, and the capacity of the channel isshared by the second device and the at least one further device forsending packets that comprise payload data and/or acknowledgementmessages.